The invention relates to a friction-disc clutch and more particularly to means which cooperate with the friction plates of the clutch halves for holding them apart on clutch disengagement. The invention is particularly used in the context of a wet friction disc clutch, that is, one in which oil is present between the friction plates.
In disengaged condition, the friction plates of wet friction-disc clutches connected with the driving shaft tend to drag the friction plates connected with the driven shaft. This is due to the existence of an oil film between the friction plates transmitting an undesirable residual torque between driving shaft and driven shaft. In order to reduce this torque, the friction discs have been given a semisoidally-shaped profile ensuring disconnection of the entire friction-disc package during disengagement by means of its inherent springiness.
Another method known from DE-PS No. 823 082 is to insert expansion elements between the outer friction plates rotatably fast with the clutch cage or between the inner friction plates torsionally connected with the hub which spread the friction plates of the outer package or those of the inner package when the clutch is disengaged, thus preventing them from sticking to the plates of the other package. As only one of the friction plate packages is spread by the ring-shaped expansion elements coated on both sides with a resilient, oil-resistant material, however, the non-spread friction plates of the other package in between can still stick to the friction plate surfaces of the spread package and transmit a friction torque. Another method known (e.g. from DE-AS No. 26 01 507) is to provide expansion elements both between the friction plates of the inner package and between those of the outer package so That each friction plate package is spread separately. However, this method cannot reliably prevent either sticking of one friction plate package to the other on one side or transmission of a friction torque. A variant of this solution described in DE-PS No. 33 20 977 involves a set of spring leaves pressing the outer friction plates in one direction and another set of spring leaves pressing the inner friction plates in the opposite direction so that during disengagement of the clutch the outer and inner friction plates are separated from each other. The spring leaves, however, have to be so designed that the outer and inner friction plates separated on one side are not pressed together on the other. Moreover, the spring leaves require a considerable expenditure.
U.S. Pat. No. 3,397,761 illustrates another known friction-disc clutch having only one inner friction disc (as second clutch half). For optimum separation of the two halves there are used resilient expansion elements, each of which is in contact with the inner friction plate on one hand and with an element of the first clutch half on the other hand. The expansion elements are attached to the inner friction plate. They are located at a comparatively great distance from the rotational axis of the clutch near the inner radial end of the friction surfaces. Due to this arrangement, they still produce a relatively great friction torque when sliding over the components of the first clutch half in disengaged condition. Moreover, they are liable to premature wear.